Climate Change and the Amazon Rainforest

Climate change may have a significant impact on the Amazon, according to a number of studies conducted since the mid-1990's.

Of particular concern is the link between sea temperatures in the tropical Atlantic and drought in the Amazon. As the tropical Atlantic warms, the large parts of the Amazon may see higher temperatures and less rainfall. The changes could have cascading effects on the region's ecosystem, killing trees and leaving forests more vulnerable to fire. Some models forecast a transition towards seasonal forests and savannas toward the end of the century, as climate warms.

2005: a peak at the future?

2005 is viewed by some researchers as a precursor to the impact climate change could have in the Amazon. In 2005 the Amazon experienced the worst drought in memory. As rivers dried up, remote communities were isolated while commerce slowed to a standstill. Thousands of square kilometers of land burned for months on end, releasing more than 100 million metric tons of carbon into the atmosphere.

At the time of the drought scientists observed an apparent correlation between sea surface temperatures in the Atlantic Ocean and precipitation in the Amazon. In 2008 Dr. Jose Marengo and colleagues from Brazil's Instituto Nacional de Pesquisas Espaciais (INPE) and the Instituto de Aeronáutica e Espaço (IEA), confirmed that "the 2005 drought was linked not to El Niño as with most previous droughts in the Amazon, but to warming sea surface temperatures in the tropical North Atlantic Ocean."

How drought affects the Amazon

In 2009 a team of 68 researchers across 13 countries and 40 institutions presented an analysis of the 2005 Amazon drought. They found that rainfall-starved tropical forests lose massive amounts of carbon due to reduced plant growth and dying trees. The drought—and associated fires—resulted in a net flux of 5 billion tons of carbon dioxide (CO2) into the atmosphere — more than the combined annual emissions of Japan and Europe.

Analyzing data from 100,000 trees in 100 forest plots, the scientists found that a 100-millimeter (4 inch) increase in water deficit triggers the loss of 2.7 tons of aboveground forest carbon per hectare. Drought also affected the species composition of the forest. Some species, especially fast-growing, light-wooded trees, are particularly vulnerable to reduced rainfall.

"Amazon drought kills selectively and therefore may also alter species composition, pointing to potential consequences of future drought events on the biodiversity in the Amazon region," the authors wrote.

Small fires, big impact

On the left, low-intensity fires open up the canopy (photo by Jos Barlow). For comparison, primary Amazon rainforest on the right (photo by R. Butler).

Drought greatly increases the incidence of fire in the Amazon rainforest, an ecosystem unaccustomed to burning. Under dry conditions, small surface fires set by landowners clearing brush and vegetation can easily spread into surrounding forests areas, burning leaf litter and seedlings. While flames from these fires rarely reach above knee-height, they inflict considerable damage. Research led by Jos Barlow and Carlos A. Peres has shown that forests affected by these small fires on more than one occasion can experience almost a complete turnover in their species composition.

Future projections

Future projects paint a dire outlook for the Amazon between the effects of climate change and continuing deforestation. In 2008 Dan Nepstad and colleagues laid out a bleak scenario with 31 percent of the Amazon rainforest deforested and 24 percent damaged by drought or logging by the year 2030. The researchers estimated that a 10 percent drop in rainfall will result in drought damage to an additional 4 percent of the forests.

"The economic, ecological and climatic systems of the Amazon may be interacting to move the forests of this region towards a near-term tipping point," Nepstad and colleagues wrote. "In this scenario, the growing profitability of deforestation-dependent agriculture and cattle ranching provides an expanding frontier of forest fragmentation and ignition sources that inhibits rainfall as forests are replaced by fields and pastures and as fires fill the late dry season atmosphere with aerosols."

"Forests damaged by drought, logging, fragmentation and previous fire burn repeatedly as tall canopy tree species are gradually replaced by coppicing trees, grasses and other high-biomass plants. These local and regional processes are exacerbated when sea surface anomalies and extreme weather events cause severe drought episodes and the burning of vast forested landscapes. Global warming reinforces these trends by elevating air temperatures, increasing dry season severity and increasing the frequency of extreme weather events."

Amazon and climate change

The Amazongate fiasco
(02/03/2010) A claim published in the Sunday Times over the veracity of a statement published in an Intergovernmental Panel on Climate Change (IPCC) report may land the British newspaper in hot water. On Sunday, Jonathan Leake, Science & Environment Editor of the Sunday Times, accused the IPCC of making a "bogus rainforest claim" when it cited a report warning that up to 40 percent of the Amazon could be "drastically" affected by climate change. Climate change skeptics immediately seized on "Amazongate" as further evidence to discredit the IPCC just two weeks after it was found to be using shoddy glacier data in its 2007 climate assessment.

(03/05/2009) Drought in the Amazon is imperiling the rainforest ecosystem and global climate, reports new research published in Science. Analyzing the impact of the severe Amazon drought of 2005, a team of 68 researchers across 13 countries found evidence that rainfall-starved tropical forests lose massive amounts of carbon due to reduced plant growth and dying trees. The 2005 drought — triggered by warming in the tropical North Atlantic rather than el Niño — resulted in a net flux of 5 billion tons of carbon dioxide (CO2) into the atmosphere — more than the combined annual emissions of Japan and Europe — relative to normal years when the Amazon is a net sink for 2 billion tons of CO2.

(02/11/2009) Changes in rainfall resulting from climate change may drive the parts of Amazon rainforest toward seasonal forests rather than savanna, argue researchers writing in the Proceedings of the National Academy of Sciences

(07/31/2008) Between June 2000 and June 2008, more than 150,000 square kilometers of rainforest were cleared in the Brazilian Amazon. While deforestation rates have slowed since 2004, forest loss is expected to continue for the foreseeable future. This is a look at past, current and potential future drivers of deforestation in the Brazilian Amazon.

(03/03/2008) With some models forecasting significant change in the Amazon rainforest over the next century, it has been unclear whether the temperature and precipitation data upon which the projections are made is accurate. Now, new research by Rafael Rosolem of the University of Arizona, shows that data associated with the Large-scale Biosphere-Atmosphere Experiment in Amazon (LBA) -- an international research initiative focusing on how changes in land use and climate will affect the biological, physical, and chemical functioning of Amazonia -- is representative of normal climatology for the region. In other words, during most of the LBA data collection period, the data was not taken during severe drought or extreme wet periods.

(02/27/2008) More than half the Amazon rainforest will be damaged or destroyed within 20 years if deforestation, forest fires, and climate trends continue apace, warns a study published in Philosophical Transactions of the Royal Society B. Reviewing recent trends in economic, ecological and climatic processes in Amazonia, Daniel Nepstad and colleagues forecast that 55 percent of Amazon forests will be "cleared, logged, damaged by drought, or burned" in the next 20 years. The damage will release 15-26 billion tons of carbon into the atmosphere, adding to a feedback cycle that will worsen both warming and forest degradation in the region. While the projections are bleak, the authors are hopeful that emerging trends could reduce the likelihood of a near-term die-back. These include the growing concern in commodity markets on the environmental performance of ranchers and farmers; greater investment in fire control mechanisms among owners of fire-sensitive investments; emergence of a carbon market for forest-based offsets; and the establishment of protected areas in regions where development is fast-expanding.

(02/27/2008) Small fires have a big impact in the Amazon rainforest, report researchers writing in Philosophical Transactions of the Royal Society B. The findings suggest a dire future for Earth's largest rainforest.

(02/25/2008) Climate models increasingly forecast a dire future for the Amazon rainforest. These projections are partly based on recent research that has linked drought in the Amazon to sea surface temperatures in the tropical Atlantic. As the tropical Atlantic warms, the southern Amazon -- the agricultural heartland of Brazil -- may see higher temperatures and less rainfall.

(02/25/2008) If past conditions are any indication of future conditions, the Amazon rainforest may survive considerable drying and warming caused by global warming, argue researchers in a paper published in Philosophical Transactions of the Royal Society B.

(02/21/2008) A new study shows that large-scale degradation of the Amazon, either through drying or continued deforestation, would have global consequence, including worsening climate change, causing regional vegetation shifts, and increasing dust in the atmosphere.

(02/20/2008) One of the worst droughts on record in the Amazon was caused by high temperatures in the Atlantic rather than el Nino. The research, published in Philosophical Transactions of the Royal Society B, suggests that human-driven warming is already affecting the climate of Earth's largest rainforest.

(01/23/2008) Cattle ranching, industrial soy farming, and logging are three of the leading drivers of deforestation in the Brazilian Amazon. As commodity prices continue to rise, driven by surging demand for biofuels and grain for meat production, the economic incentives for developing the Amazon increase. Already the largest exporter of beef and the second largest producer of soy - with the largest expanse of "undeveloped" but arable land of any country - Brazil is well on its way to rivaling the U.S. as the world's agricultural superpower. The trend towards turning the Amazon into a giant breadbasket seems unstoppable. Nevertheless the decision at the U.N. climate talks in Bali to include "Reducing Emissions From Deforestation and Degradation" (REDD) in future climate treaty negotiations may preempt this fate, says Dr. Daniel Nepstad, a scientist at the Woods Hole Research Institute.

(11/07/2007) While the mention of Amazon destruction usually conjures up images of vast stretches of felled and burned rainforest trees, cattle ranches, and vast soybean farms, some of the biggest threats to the Amazon rainforest are barely perceptible from above. Selective logging -- which opens up the forest canopy and allows winds and sunlight to dry leaf litter on the forest floor -- and 6-inch high "surface" fires are turning parts of the Amazon into a tinderbox, putting the world's largest rainforest at risk of ever-more severe forest fires. At the same time, market-driven hunting is impoverishing some areas of seed dispersers and predators, making it more difficult for forests to recover. Climate change -- an its forecast impacts on the Amazon basin -- further looms large over the horizon.

(10/22/2007) By some measures, forest fires in the Amazon are at near-record levels, according to analysis Brazilian satellite data by mongabay.com. A surge in soy and cattle prices may be contributing to an increase in deforestation since last year. Last year environmentalists and the Brazilian government heralded a sharp fall in deforestation rates, the third consecutive annual decline after a peak in 2004. Forest loss in the 2006-2007 season was the lowest since record-keeping began in the late in 1970s. While the government tried to claim credit for the drop, analysts at the time said that commodity prices were a more likely driver of slow down: both cattle and soy prices had declined significantly over the previous months.

(06/03/2007) The Amazon basin is home to the world's largest rainforest, an ecosystem that supports perhaps 30 percent of the world's terrestrial species, stores vast amounts of carbon, and exerts considerable influence on global weather patterns and climate. Few would dispute that it is one of the planet's most important landscapes. Despite its scale, the Amazon is also one of the fastest changing ecosystems, largely as a result of human activities, including deforestation, forest fires, and, increasingly, climate change. Few people understand these impacts better than Dr. Daniel Nepstad, one of the world's foremost experts on the Amazon rainforest. Now head of the Woods Hole Research Center's Amazon program in Belem, Brazil, Nepstad has spent more than 23 years in the Amazon, studying subjects ranging from forest fires and forest management policy to sustainable development. Nepstad says the Amazon is presently at a point unlike any he's ever seen, one where there are unparalleled risks and opportunities. While he's hopeful about some of the trends, he knows the Amazon faces difficult and immediate challenges.

(05/08/2007) The amount and distribution of above ground biomass (or the amount of carbon contained in vegetation) in the Amazon basin is largely unknown, making it difficult to estimate how much carbon dioxide is produced through deforestation and how much is sequestered through forest regrowth. To address this uncertainty, a team of scientists from Caltech, the Woods Hole Institute, and INPE (Brazil's space agency), have developed a new method to determine forest biomass using remote sensing and field plot measurements. The researchers say the work will help them better understand the role of Amazon rainforest in global climate change.

(03/14/2007) Fires are nothing new to the Amazon reports a study published in the journalBiotropica. Analyzing soils in the eastern Amazon, a team of scientists led by David S. Hammond of NWFS Consulting, has found evidence of forest fires dating back thousands of years. While the origin of these fires is unclear, the authors propose intriguing scenarios involving pre-Colombian human populations and ancient el Nino events which could have so dried rainforest areas that they became more prone to forest fires.

(10/23/2006) For the Amazon, there is an immense threat looming on the horizon: climate change could well cause most of the Amazon rainforest to disappear by the end of the century. Dr. Philip Fearnside, a Research Professor at the National Institute for Research in the Amazon in Manaus, Brazil and one of the most cited scientists on the subject of climate change, understands the threat well. Having spent more than 30 years in Brazil and now recognized as one of the world's foremost experts on the Amazon rainforest, Fearnside is working to do nothing less than to save this remarkable ecosystem. Fearnside believes saving the Amazon will require a fundamental shift in perception where the Amazon is recognized as an asset beyond the current price of mahogany, soybeans, or cattle, where its value is only unlocked by its destruction. The Amazon is far worth more than this he says. It can play a key role in fighting climate change while providing economic sustenance for millions through sustainable agriculture and rational utilization of its renewable products. It can serve as a storehouse for biodiversity while at the same time ensuring reliable water supplies and moderating regional temperature and precipitation. In short, maintaining the Amazon as a viable ecosystem makes sense economically and ecologically -- it is in our best interest to preserve this resource while we still can.

(10/17/2006) The world's tropical rainforests are in trouble. Spurred by a global commodity boom and continuing poverty in some of the world's poorest regions, deforestation rates have increased since the close of the 1990s. The usual threats to forests -- agricultural conversion, wildlife poaching, uncontrolled logging, and road construction -- could soon be rivaled, and even exceeded, by climate change and rising levels of carbon dioxide in the atmosphere. Understanding these threats is key to preserving forests and their ecological services for current and future generations. William F. Laurance, a distinguished scholar and president of the Association for Tropical Biology and conservation (ATBC) -- the world's largest scientific organization dedicated to the study and conservation of tropical ecosystems, is at the forefront of this effort.

(03/22/2006) Scientists today warned that 40 percent of the Amazon rainforest could be lost by 2050 due to agricultural expansion unless strict measures are taken to protect the world's largest tropical forest.

(12/11/2005) The worst drought ever recorded in the Amazon continues according to an update from The New York Times. The drought has turned rivers into grassy mud flats, killed tens of millions of fish, stranded hundreds of communities, and brought disease and economic despair to the region.